The purpose of this project is the development of a clinical, non-invasive monitor of tissue blood flow by analysis of the spectrum of Doppler scattered laser light. The NIH Laser Doppler Blood Flow Monitor has been demonstrated to be highly portable and clinically convenient with the new flexible 4m fiber optic probes and photodiode detection system. The probes withstand sterilization procedures and mechanical insult well and are suitable for operating room patient study. The linearity of the flow analysis processor has been demonstrated in a variety of tissues and clearly resolves physiologic flow changes including instantaneous pulsatile flow in the microcirculation. Muscle blood flow in over 50 patients with neuromuscular disease has been studied and preliminary data suggest that post occlusive reactive hyperemia responses may be primary or secondary indicators of disease state. Studies of scleroderma patients' skin blood flow have shown markedly reduced flows in advanced scleroderma with very high flows at telangiectasia. Clinical applications being developed for the instrument are: allergy testing - quantitative methodology, periocular blood flow as indicator of external-internal carotid artery flow and implied flow to circle of Willis.